The general objective of the proposed study is to improve ability to identify infants at increased risk for SIDS. Our study plan consists of identification of risk groups, based on current epidemiologic and physiologic data, as subsequent siblings of SIDS, "near miss" for SIDS, premature infants born to teenage mothers and controls. We will study the infants longitudinally during the ages of highest risk for SIDS to detect developmental patterns. We will focus on cardiorespiratory variables during sleep states since respiratory control mechanisms vary with sleep state. Oxygen levels will be continuously recorded during monitoring sessions because the ultimate significance of altered breathing patterns depends on their effect on blood gas level. Specific variables of respiratory rate, heart rate, apnea, asynchronous breathing will be examined in relation to risk for SIDS, age and sleep state. Each variable has been selected because it should provide support for the hypoxia model for risk for SIDS. In infants with selected abnormal respiratory patterns, pulmonary function studies will be performed in order to clarify the underlying mechanisms.